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參數資料
| 型號： | LM8300 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Four Wire Resistive Touchscreen Controller with Brownout |
| 中文描述： | 四線電阻式觸摸屏控制器掉電 |
| 文件頁數： | 14/20頁 |
| 文件大?。?/td> | 327K |
| 代理商： | LM8300 |
12.0 Averaging Algorithm
(Continued)
12.2 FOCUS ALGORITHM
The focus algorithm removes some inaccuracy and noise
that could cause the coordinate to differ only by a couple of
pixels. The focus algorithm is used to eliminate the "jittering"
effect of the pointer when the pointer is stationary.
The focus algorithm compares the value of the previous
stored value to the value passed from the delta algorithm
and determines if the difference is greater than or equal to
the Set Focus Value. If the difference is greater or equal to
the value in Set Focus Value then the new coordinate is sent
out through the UART and stored as the previous value. If
the difference is less than the Set Focus Value then the
value is discarded and the stored valued is set through the
UART.
The amount of difference between the new coordinate and
the old coordinate is set in the Set Focus Value. This value
can be from 0-63 with a value of 0 disabling the focus
algorithm. The factory default is 4.
12.3 COMMUNICATION MODES
Liftoff
When set to the liftoff mode, the controller only sends data
through the UART on liftoff. The controller continuously
samples the touchscreen as long as there is a touch de-
tected on the touchscreen but only the last coordinate is sent
out to the UART.
Touchdown
When set to the touchdown mode, the controller only sends
data through the UART on touchdown. The controller con-
tinuously samples the touchscreen as long as there is a
touch detected on the touchscreen but only the first coordi-
nate is sent out to the UART.
Streaming
When set to the streaming mode, the controller continuously
sends data through the UART as long as there is a touch
detected on the touchscreen.
13.0 Brownout Reset
The device is initialized when the RESET pin is pulled low or
the On-chip Brownout Reset is activated.
The RESET input initializes the device when pulled low. The
RESET pin must be held low for a minimum of 0.5μs for the
LM8500 and a minimum of 1.5μs for the LM8300 to guaran-
tee a valid reset. Reset should also be wide enough to
ensure crystal start-up upon power-up. The R/C circuit
shown in
Figure 3
is an optional circuitry that will provide a
delay 5 times (5x) greater than the power supply.
When enabled, the device generates an internal reset as
V
rises. While V
is less than the specified brownout
voltage (V
), the device is held in the reset condition for t
id
= 120-128 μs for the LM8500 and t
= 360-384 μs for the
LM8300. Once the t
reaches zero, the internal reset is
released and the controller resume normal operation. This
internal reset will perform the same functions as external
reset. Once V
is above the V
and t
id
reaches zero,
instruction execution begins. If, however, V
drops below
the selected V
, an internal reset is generated, and t
is set
to 120-128 μs for the LM8500 and 360-384 μs for the
LM8300. The device now waits until V
is greater than V
,
at which time the countdown starts over. When enabled, the
functional operation of the device, at frequency, is guaran-
teed down to the V
bor
level.
One exception to the above is that the brownout circuit will
insert a delay of approximately 3 ms on power up or any time
the V
CC
drops below a voltage of about 1.8V. The device will
be held in Reset for the duration of this delay before t
id
starts
count down. This delay starts as soon as the V
CC
rises
above the trigger voltage (approximately 1.8V). This behav-
ior is shown in
Figure 4
.
In Case 1, V
CC
rises from 0V and the on-chip RESET is
undefined until the supply is greater than approximately
1.0V. At this time the brownout circuit becomes active and
holds the device in RESET. As the supply passes a level of
about 1.8V, a delay of about 3 ms (td) is started and t
is
preset with 120-128 μs for the LM8500 or 360-384 μs for the
LM8300. Once V
is greater than V
bor
and td has expired,
t
id
starts to count down.
Case 2 shows a subsequent dip in the supply voltage which
goes below the approximate 1.8V level. As V
drops below
V
, the internal RESET signal is asserted. When V
rises
back above the 1.8V level, td is started. Since the power
supply rise time is longer for this case, td has expired before
V
rises above V
bor
and t
id
starts immediately when V
CC
is
greater than V
bor
.
Case 3 shows a dip in the supply where V
drops below
V
bor
, but not below 1.8V. On-chip RESET is asserted when
V
goes below V
bor
and t
id
starts as soon as the supply
goes back above V
bor
.
20037205
FIGURE 3. Optional Reset Circuit using External Reset
L
www.national.com
14
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| LM8300ILQ9 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Four Wire Resistive Touchscreen Controller with Brownout |
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